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Understanding Insecticidal Soaps and Detergents

Don’t Get “Lathered:” Understanding Insecticidal Soaps and Detergents

Continuation of Understanding Insecticidal Soaps and Detergents

There is a misconception that any “soap” or “detergent” can be used as a pesticide (insecticide or miticide). Although, as already discussed, only a few select soaps have insecticidal or miticidal properties, many common household soaps and detergents including Palmolive®, Dawn®, Ivory®, Joy®, Tide®, and Dove®, which are unlabeled pesticides, have some activity on a number of soft-bodied insect and mite pests when applied to plants as a 1% or 2% aqueous solution. However, reliability is less predictable than insecticidal soaps formulated as pesticides.

Examples of studies that have demonstrated the effectiveness of various dishwashing liquids and detergents on certain insect and mite pests are presented below:

• Palmolive®, Dawn®, Joy®, Ivory®, and Dove® reduced populations of the cabbage aphid (Brevicoryne brassicae), green peach aphid (Myzus persicae), sweet potato whitefly (Bemisia tabaci), and the twospotted spider mite on a variety of vegetable crops.
• Dawn Ultra® dishwashing liquid was effective in controlling the German cockroach (Blattella germanica) causing 100% mortality.
• Ivory® liquid dishwashing soap at 0.4% to 3.0% concentrations provided control of aphids, psyllids, and spider mites.
• Ivory® liquid dishwashing soap was active against aphids, psyllids, spider mites, and thrips at 1% and 2% concentrations.
• New Day® dishwashing detergent when used at 2.0 ml/L was effective in controlling whiteflies providing 95% mortality of the sweet potato B-biotype whitefly (Bemisia tabaci) nymphs. The active ingredient in New Day is cocamide DEA and dodecylbenzene sulphonic acid.
• Ivory® liquid dishwashing soap and Tide® detergent reduced populations of aphids, citrus red mite (Panonychus citri), greenhouse thrips (Heliothrips haemorrhoidalis), and psyllids on landscape plants.

Despite these examples, dishwashing liquids and laundry detergents are primarily designed to dissolve grease from dishes and clean clothes — not kill insect and/or mite pests. These materials may cause phytotoxicity by dissolving the waxy cuticle on leaf surfaces. Although many plant leaves (primarily foliage plants) possess a thickened cuticle and some flowers are waxy there is still a risk of phytotoxicity. Registered commercially-available insecticidal soaps are less likely to dissolve plant waxes compared to household cleaning products. Dishwashing liquids and laundry detergents, like insecticidal soaps, lack any residual activity and thus more frequent applications are required. However, too frequent applications will damage the leaves or flowers of certain plant species. In addition, detergents are chemically different from soaps. In fact, many hand soaps are not really pure fatty acids. Most importantly, these solutions are not registered pesticides (again, insecticides or miticides). Furthermore, soap companies don’t intend for their products to be used against insect or mite pests because they have not gone through the Environmental Protection Agency (EPA) registration process.

The type of fatty acid, length of the carbon-based fatty acid chain, and concentration in many laundry and dish soaps is not known. Also, the insecticidal effectiveness of these products may be compromised by the presence of coloring agents or perfumes. This often times leads to inconsistent results. Certain laundry and dish soaps will precipitate in “hard” water thus reducing their effectiveness.

Despite the activity of some dishwashing liquids and laundry soaps on insect and mite pests, their use should be avoided on plants primarily because they are not registered pesticides as they don’t have an EPA Registration Number. Even more important is that a pest control company will generally stand behind a product when there is a problem. If a dish or laundry soap is used and plants are injured — there is no recourse. As such, always use an insecticidal soap to deal with insect and mite pests encountered in greenhouses and/or conservatories.

About the Author: Dr. Raymond A. Cloyd is an Associate Professor and Extension Specialist in Ornamental Entomology and Integrated Pest Management for the Department of Entomology at Kansas State University (KSU). A “Bugologist.” He is both knowledgeable and approachable. Dr. Cloyd has previously published Pesticide Compatibility: Is It Really Possible? and Can Pests Become Resistant to Natural Enemies? in our Bug Blog.

Additional Resources

In addition to the references list supplied by the author, here are additional resources that may compliment this article.

1. Learn more about noted arthropod pests (this site).
2. Learn more about noted natural enemies (this site).
3. Learn more about noted Q-Biotype Whitefly (this site).
4. See glossary for referenced terminology (this site).

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